1. Technical Field
The present invention relates to packaging apparatus including a rotary jaw device and to a method of making packages.
2. Description of Related Art
It is known to employ vertical form, fill, and seal (VFFS) packaging apparatus to produce packages, in the form of bags, pillow packs or pouches of products, such as snack foods. A tubular film, having been formed from a roll of packaging film of heat sealable plastic material which has been longitudinally sealed, is fed intermittently through a jaw device. The film forms a flattened tube at the jaw device. The jaw device forms a pair of vertically spaced hermetic heat seals extending transversely across the tube, the seals being located between vertically adjacent packages. The jaw device also cuts through a middle portion, located between the hermetic seals, extending across the tube which separates a lower sealed package containing the packaged product from an upper unsealed package.
In this way, a lower hermetic seal forms the upper seal of the lower package, and an upper hermetic seal forms the lower seal of the upper package. The upper package is then filled with product, the tube is advanced downwardly through the jaw device, and then the cycle is repeated when the upper edge of the upper package, and the lower edge of the following package, is disposed between the jaws of the jaw device.
There are several known principles of operation of such jaws of a vertical, form, fill, and seal (VFFS) packaging apparatus. One class of jaw devices utilises a continuous rotary jaw motion, which is illustrated with reference to FIGS. 1 and 2.
Referring to FIG. 1, in such a jaw device 10, a knife 12 is disposed on one side of the flattened, longitudinally sealed tube 14, and a hardened reaction pad or anvil 16 is disposed on the opposite side of the tube 14, with the tube located between the knife 12 and anvil 16. The knife 12 is urged under pressure against the anvil 16 to cut through the film of the tube 14, trapped between the knife blade 18 and the anvil 16, by a pressured crush-cutting action.
The knife 12 and the anvil 16 both rotate in phase and in opposite rotational directions as shown by the arrows in FIG. 1 so that the knife 12 and the anvil 16 engage so as to cut packaging film material, in the form of a flattened tube as described below, centrally located therebetween.
The knife 12 is rotated about an axis X orthogonal to the longitudinal direction L of the tube 14 and parallel to the surface of the anvil 16 and the cutting edge 20 of the blade 18. Although not illustrated, plural knives 12 may be mounted about a common shaft disposed along axis X and mutually angularly separated, so that for each cycle of rotation of the common shaft, plural cuts are made by respective knives 12. Plural anvils 16 would be correspondingly provided.
As also shown in FIGS. 2 and 3, the elongate knife 12 is mounted in an elongate holder 21 in the form of a mounting block. For clarity of illustration, some dimensions and angles are exaggerated in FIGS. 2 and 3.
The lower portion of the knife 12 is received in an elongate recess 30 in the elongate holder 21 and securely fixed therein. The cutting action of the knife 12 is progressive, so that during the continuous rotation of the knife 12 in holder 21, initially one longitudinal end 22 of the knife 12 first contacts the anvil 16 and subsequently the contact point therebetween progresses along the cutting edge 20 of the blade 18 towards the other longitudinal end 24 of the knife 12. To achieve such progressive cutting action, as shown in FIGS. 2 and 3, the cutting edge 20 of the blade 18 is ground at an angle α to the plane of the knife 12. Typically, the angle α is 2 degrees. Accordingly, as the rotary contact progresses, the whole width of the flattened tube 14 is not cut through simultaneously, but instead point contact of the knife blade 18 transitions across the tube 14 as the rotary action progresses. The progressive cutting action is similar to that of a rotary blade of a cylinder lawnmower.
Elongate heat seal devices 26, 28 are disposed either in the anvil 16 and/or in the elongate holder 21 for the knife so that transverse hermetic seals 32, 34 are formed in the flattened tube 14 on opposite sides of the transverse cut 36 made by the knife 12. The heat seal devices 26, 28 may take a number of forms, typically transversely extending mating ridges and grooves formed in the opposed surfaces of the anvil 16 and the elongate holder 21.
As shown in FIG. 2, the knife 12 and the heat seal devices 26, 28 are mutually parallel and also parallel to the sides 40, 42 of the elongate holder 21 which is orthogonal to the longitudinal direction L. Thus, when the longitudinal direction is conventionally oriented vertically, the knife 12 and the heat seal devices 26, 28 are horizontal.
The known rotary jaw device provides an effective heat sealing and cutting mechanism, which reliably forms hermetic seals at the opposite ends of a package and with adjacent packages being reliably separated by the action of the knife.
However, there is an increasing need for product manufacturers to reduce the amount of packaging material associated with their products, and in particular not only to reduce packaging costs but also to reduce the carbon footprint, expressed in tonnes of carbon dioxide emissions, of the packaging material and/or the packaging operation.
The known rotary jaw device forms hermetic seals which are rather wide, in the longitudinal direction of the tube, and also there is material wastage between adjacent hermetic seals, because a portion of the film material of the tube which is cut through by the rotary cutting action of the knife must be provided between the adjacent hermetic seals.
Accordingly, there is a need in the art for a rotary jaw device for a packaging apparatus, and to a method of making packages, which can permit the amount of packaging material to be reduced, together with the associated packaging costs and carbon footprint, i.e. carbon dioxide emissions, while still achieving effective hermetic seals at the opposite ends of a package.